The use of organolithium compounds as initiators in polymerization of organic monomers is well known in the art. A particular use for the organolithium initiators is in the production of block copolymers having at least two polymeric block which differ in properties. Many conventional block copolymers are polymers of at least one block of polymerized vinylaromatic hydrocarbon, e.g. styrene, and at least one block of polymerized conjugated alkadiene, e.g., butadiene. Such polymers typically have a relatively narrow molecular weight distribution and, to the extent a block is produced from an alkadiene, the polymer will contain ethylenic unsaturation.
For some applications, it would be useful to produce block copolymer wherein one type of block has an unbranched, saturated polymeric chain which is terminally connected to adjacent blocks. It is very difficult, however, to produce this type of block directly by anionic polymerization. It is known to produce this type of block indirectly by selective hydrogenation of a block of polymerized alkadiene, but such indirect preparation introduces additional process steps and will be influenced by the type and configuration of the original polyalkadiene block. Moreover, this method of synthesis is not useful for the production of a block copolymer containing a saturated polyolefin block and, as a second type of block, polyalkadiene.
In Japanese Patent Application J5-9179-527-A, a method is disclosed for the production of a polypropylene-polystyrene block copolymer. A halogenated polypropylene is reacted with a lithiated polystyrene species produced by anionic polymerization of styrene. The process necessarily introduces halogen into the product mixture and is only useful for the production of diblock polymers.
Japanese Patent Application J6-2054-712-A discloses the preparation of modified polyolefins. An .alpha.-olefin is polymerized in the presence of a Ziegler-Natter catalyst. The polyolefin product is reacted with an organolithium compound and then copolymerized with added styrene. The polyolefin production is effected in the presence of a heterogenous catalyst system and the product has a broad molecular weight distribution with relatively little of the ethylenic unsaturation present in the terminal segment of the polymer. Metallation of the polyolefin results in a random arrangement of metal moieties and use of the metallated polymer as an ionic polymerization initiator results in production of a mixture of polymeric species with only a small portion thereof being of a linear type. Similar results are obtained by the process disclosed in German published Patent Application 1 595 359.
It would be of advantage to have a process for the production of block copolymers containing saturated polyolefin blocks which are linear and attached to any adjacent block through the terminal portion of the polyolefin block.